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M2 Technical Topics > N55 Engine / Drivetrain / Exhaust / Bolt-ons / Tuning > Active Autowerke | F87 M2 Signature Exhaust Release

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      12-31-2019, 05:45 PM   #23
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Originally Posted by David@ActiveAutowerke View Post
We are working on a catted downpipe and it's currently in longevity testing. I can't say exactly which cat it is right now but it's not an HJS core. We do plan on having an option for it to mate in to our 3.5" system.

As you know, volume is directly related to velocity and velocity is what's important which is why the two smaller pipe design you're referring to works. That said, two smaller pipes with a combined volume larger than a single 3.5" will create more friction because of surface area. You'd be better off stepping to a smaller single pipe if you were really concerned with exhaust velocity at the rear of the exhaust, although I can see that hurting top end power eventually. We do have two bends at the rear, one with a tighter radius than the other as pictured below. At the rear of the system the exhaust is much cooler and therefore a bit slower as well, so we haven't noticed this being an issue at all. On a turbocharged engine, power is made at the turbo exit (downpipe) and beginning of the exhaust system when exhaust velocity is high.
Why didnt you guys go with HJS core for the DP? Just curious. I see you went with GESi (Global Emissions Systems Inc.)? Why them? Equivalent quality?
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